The lower Mississippi is in no way a natural river anymore. A law instituted in 1724 by a French colonial governor, whose name was Perrier, of all things, demanded that early homeowners in New Orleans raise the low natural levees upon which they all built. Three year later, Perrier declared the little city floodproof.
So there you have it. Do not blame Bush. Blame France.
Not really. The situation is a deal more complex than that. But it does seem to be true that once they decided on living lower than the Mississippi River, they found that the methods they chose to protect themselves from it only served to make it rise ever higher into the air, and themselves to sink lower and lower.